In accordance with a reduction of thickness and weight in electronic devices such as display panel, solar cell, thin-film secondary battery or the like, the reduction of sheet thickness of substrate (first substrate) such as glass sheet, resin sheet, metal sheet or the like used for these electronic devices is required.
However, when the thickness of the substrate is thin, since a handling property of the substrate deteriorates, it is difficult to form a functional layer (thin film transistor (TFT), color filter (CF)) for the electronic device on a surface of the substrate.
Therefore, a method is proposed in which a reinforcing plate (second substrate) is attached to the rear surface of the substrate to configure a laminate in which the substrate is reinforced with the reinforcing plate, and to form a functional layer on the surface of the substrate in the state of the laminate (refer to PTL 1). In this method, since the handling property of the substrate is improved, the functional layer can be favorably formed on the surface of the substrate. The reinforcing plate is peeled off from the substrate after the functional layer is formed.
As a reinforcing plate peeling method is performed by, for example, curving and deforming the reinforcing plate or the substrate, or both thereof in a direction to separate them from each other from one of the two corner portions located on a diagonal line of the rectangular laminate to the other thereof. Here, in order to smoothly perform peeling, a peeling starting portion is prepared at one corner portion of the laminate. The peeling starting portion is prepared by inserting a knife with a predetermined amount between the substrate and the reinforcing plate from the end surface of the laminate, and forming the peeling starting portion in a predetermined area of one corner portion as in PTL 1.